Method to enhance microbial gas production from unconventional reservoirs and kerogen deposits

ABSTRACT

A biostimulation method comprising injecting sulfur dioxide into water producing H + , SO 2 , SO 3   = , HSO 3   − , dithionous acid (H 2 S 2 O 4 ), and other sulfur intermediate reduction products in sulfurous acid, and then applying the sulfurous acid at the oxidation reduction potential required to biostimulate either aerobic or anaerobic organisms at the active margins of the black shale and coal bed deposits at a pH sufficient to reduce bicarbonate and carbonate buildup to a) increase CO 2  production to drive the production of methane by chemoautotrophic assimilation of CO 2  by hydrogen consuming methanogens, b) increase porosity and flows through the black shale and coal bed deposits, and c) provide SO 2 , SO 3   − , HSO 3   − , and dithionous acid (H 2 S 2 O 4 ) and other sulfur intermediate reduction products to provide soluble nutrients with bicarbonates and carbonate conducive to the growth of microbial consortia under either aerobic or anaerobic conditions to stimulate syntrophic bacteria and methanogenic archaea to produce methane.

BACKGROUND OF THE INVENTION

1. Related Applications

This application is a continuation-in-part of the “Method to Enhance Microbial Gas Production from Unconventional Reservoirs and Kerogen Deposits” patent application, Ser. No. 13/385,443 filed Feb. 21, 2012.

2. Field

This invention relates to methane and petroleum production. More particularly, it relates to the production of methane and petroleum via biostimulation of microbial metabolism from the margins of a basin where the organic matter is less mature and hydrologic flow systems are active.

3. State of the Art

Unconventional gas deposits, such as those produced from coal beds and shales containing kerogen are new sources of methane gas. Black shales and coal beds contain carbon deposits where microbial methanogenis and modification of thermogenic gas is present at the shallower margins of a basin where the organic matter is less mature and hydrologic flows are present. These deposits contain kerogen, which is a mixture of organic chemical compounds that make up a portion of the organic matter in sedimentary rocks. It is insoluble in normal organic solvents because of the huge molecular weight (upwards of 1,000 Daltons) of its component compounds. The soluble portion is known as bitumen. Production of oil and gas from kerogen is usually accomplished under geophysical pressure and temperature conditions at deeper depths (thermogenic gas play), over long periods of time where organic material experiences more thermal cracking. When heated to the right temperatures in the Earth's crust, some types of kerogen release crude oil or natural gas. For example, oils are formed around 60-160° C. and gas is formed around 150-200° C., depending on how quickly the source rock is heated.

Kerogen is formed from the decomposition and degradation of living matter, such as diatoms, planktons, spores and pollens. In the break-down process, large biopolymers from proteins and carbohydrates begin to partially or completely dismantle. Under pressure, these dismantled components can form new geopolymers, which are the precursors of kerogen.

The formation of geopolymers account for the large molecular weights and diverse chemical compositions associated with kerogen. The smallest geopolymers are the fulvic acids, the medium geopolymers are the humic, and the largest geopolymers are the humins. When organic matter is contemporaneously deposited with geologic material, subsequent sedimentation and progressive burial or overburden provides sufficient geothermal pressures over geologic time to become kerogen. Changes such as the loss of hydrogen, oxygen, nitrogen, and sulfur and other functional group result in isomerization and aromatization at increasing depths or burial eventually producing petroleum or methane gases.

This geophysical production of petroleum and methane, gas from black shale and coal bed deposits containing kerogen is extremely slow. Consequently, new sources of natural gas require enhancing microbial gas from unconventional reservoirs. The present method described below expedites the production of petroleum and methane from unconventional gas play. It biostimulates certain bacteria and micro-organisms with sulfurous acid delivered nutrients to break down kerogen and other organic matter into petroleum and methane.

Clement et al (WO 2011/153467 A2, claiming priority to Jun. 4, 2010; cited on PTO-982 mailed Jan. 7, 2013) teaches introducing compositions in situ to enhance the biogenic production of methane in coal and shale deposits containing kerogen in coal seams and coal be methane wells. Clement et al.'s approach is to add various combination of amendments as stimulants for microbial respiration screened for methane production using gas chromatography (paragraph 034 last three lines). These stimulants are listed in paragraphs 52-54, and include a wide range of components ranging from vanadium to yeast extract to sulfuric acid with different oxidation states to stimulate the microbial organisms to produce methane via hydrolysis, coal depolymerization, anaerobic or aerobic degradation of polyaromatic hydrocarbons, homoacetogenesis, and methanogenisis and any combinations thereof (paragraph 54). This complex addition of multiple different stimulants is difficult to administer in the field, and requires the storage of a wide variety of different chemicals as well as gas chromatograph testing capability. Conversely, applicant's method only requires a source of sulfurous acid and air, and a conductivity meter, gas flow meter, and microbial sampling and testing equipment. The sulfurous acid oxidation reduction potential is adjusted as required to provide the required anaerobic or aerobic conditions to biostimulate the production of methane.

No anaerobic or aerobic reaction controls or concentrations are specified in Clement et al as to how to optimize methane stimulation from the different stimulants. Nor does Clement et al expressly teach:

-   -   a. biostimulating microbial populations active at margins of         coal black shale and coal bed deposits where the organic matter         is less mature.     -   b. maintaining the sulfurous acid at a pH concentration         sufficient to reduce bicarbonate and carbonate buildup         increasing the porosity and flows through the black shale and         coal bed deposits.     -   c. injecting sulfur dioxide into water producing H⁺, SO₂, SO₃ ⁼,         HSO₃ ⁻, dithionous acid (H₂S₂O₄), and other sulfur reduction         product.

Clement also fails to disclose monitoring microbial populations and changing the oxidation/reduction potential of sulfurous acid for enhancing methane production either between −50 and −150 mV creating an oxidizing solution by adding oxygen and additional acid to provide aerobic conditions for aerobic biostimulation; or between +50 and −100 mV without the addition of oxygen and additional acid to produce a reducing solution to provide anaerobic conditions for anaerobic biostimulation. Clement et al, thus fails to suggest or provide any guidance as to the conditions required fur sulfurous acid to act as a biostimulant.

Jackson et al, (US Patent Application Publication 20105/0247705 A1, cited on PTO-892 mailed Jan. 7, 2013)) is a sulfurous acid generator. It does not explicitly teach that injecting sulfur dioxide into water produces H⁺, SO₂, SO₃ ⁻, HSO₃ ⁻, dithionous acid (H₂S₂O₄) to provide microbial CO₂ gas conditions for methogens to act under anaerobic conditions.

The present method described below delivers sulfurous acid at a pH and oxidation reduction potential to stimulate natural microbial populations active at margins of black shale and coal bed deposits where the organic matter is less mature and has hydrologic flows there through under either aerobic or anaerobic conditions to increase methane gas production.

SUMMARY OF THE INVENTION

Natural alteration of organic matter into methane by microorganisms in oxygen-depleted subsurface environments is a widespread and common process called methanogenesis. The biogenic generation of methane from the molecules of kerogen is achieved by a symbiotic consortium of microorganisms. Syntrophic bacteria of the consortium break down the organic molecules through anaerobic respiration and fermentation into simple, water-soluble compounds (e.g. acetate, CO₂, H₂), which are ultimately transformed into CH₄ by methanogenic archaea. Other microorganisms produce methane under aerobic conditions.

The method comprises monitoring and measuring the methane gas production from the margins of black shale and coal bed deposits. Next, the microbial populations at the margins of black shale and coal bed deposits where the organic matter is less mature and hydrologic flows there through are active to stimulate the production of methane by delivering supplemental nutrients (a treatment referred to as “biostimulation”) with sulfurous acid. Methane production is stimulated by delivering water, acid, sulfites, sulfates, and other nutrients to the microbial consortia under either anaerobic or aerobic conditions to stimulate the syntrophic bacteria and methanogenic archae.

Under anaerobic reducing conditions,

-   -   a) denitrification occurs:         C_(a)H_(b)O_(c)+(4a′b/4−c/2)O₂→aCO₂+(2b−2a+c)H2O+(4a+b−2c)OH⁻+(2a+1/2−c)N₂     -   b) sulfate reduction occurs:         C_(a)H_(b)O_(c)+(2/5a+1/10B−1/5c)SO₄→aCO₂+(2/5−2/5a+1/5c)H2O+(2/5a+1/10b−1/5c)H2S     -   c) methanogenisis occurs:         C_(a)H_(b)O_(c)+(a−b/4−c/2)H₂O→(a/2−b/8+c/4)CO₂+(a/2+b/8−c/4)CH₄         (Buswell reaction)

The Buswell reaction results from three separate biological reactions by three different types of syntrophic microorganisms:

-   -   a) acetogenic bacteria generate acetate and hydrogen that is         toxic to themselves:

C_(a)H_(b)O_(c)+(a−c)H₂O=1/2aCH₃CO⁻ ₂+1/2aH⁺+1/2(b−2c)H₂

-   -   b) hydrogenotrophic methanogens remove the hydrogen to protect         the acetogenic bacteria:

CO₂+4H₂→CH₄+2H₂O

-   -   c) acetoclastic bacteria use the acetate to form methane and         carbon dioxide:

C_(a)H_(b)O_(c)+H⁺→CH₄+CO₂

As anaerobic conditions are generally required for the microbial consortia in deep black shale and coal bed deposits, sulfur dioxide (SO₂) is injected into water to be injected into the kerogen beds forming as weak acid to provide H⁺, SO₂, SO₃ ⁼, HSO₃ ⁻, dithionons acid (H₂S₂O₄), and other sulfur intermediate reduction products. Sulfur dioxide acts as a strong reducing agent in water and in the presence of minimal oxygen no additional acid is required to be added to insure the electrical conductivity level of the sulfur dioxide treated water is sufficient for release of electrons from the sulfur dioxide, sniffles, bisulfites, and dithionous acid to form a reducing solution. The sulfur dioxide treated water provides the oxidation/reduction potential within the black shale and coal bed for the syntrophic bacteria of the consortium break down the organic molecules through anaerobic respiration and fermentation into simple, water-soluble compounds (e.g. acetate, CO₂, H₂), which are ultimately transformed into CH₄ by methanogenic archaea.

The acetoclastic bacteria chemical reaction is also driven to the right to form more methane by the addition of the weak sulfurous acid:

CH₃CO⁻ ₂+H⁺→CH₄+CO₂.

The oxidation/reduction potential of the sulfurous acid in milivolts for anoxic conditions with no dissolved oxygen is usually between +50 and −100 mV, although the exact potential is dependent upon the consortium bacteria present.

The sulfurous acid also acts to dissolve and free up carbonates/bicarbonates to open up pores and channels in the black shale and coal beds to better deliver nutrients and carbon dioxide to the microbial consortia. Sulfurous acid is a powerful reducing agent, which removes oxygen; thereby insuring anaerobic conditions for the syntrophic bacteria and methanogenic archae. The freed up added CO₂ also drives to the right the chemoautotrophic assimilation of CO₂ by the hydrogen consuming methanogens to produce more methane:

CH₂+4H₂→CH₄+2H₂O

If sufficient microbial consortia are not present in the kerogen beds, cultures of syntrophic bacteria, and methanogenic archae may be delivered along with the sulfurous acid into the black shale and coal beds to start the methanogenesis process.

Generally, the source-rocks of interest are the Lower Jurassic black shales of the eastern Paris Basin (i.e. type II kerogens), Corings into various points within the shales are drilled to deliver the sulfurous acid at various points within the hydrologic flows of the bed. Other drill holes penetrate the bed at various points to collect the generated gases.

The presence of methane in sample culture extracts of the sulfurous acid correlates with the detection of archaea and methanogens by qPCR. Thus it may be necessary to monitor the presence of methanogens in the sulfurous acid microcosms by periodic sampling.

If other bacterial, archaeal and methanogen populations nearer the surface of black shale and coal bed deposits are involved in the production of methane or petroleum under aerobic conditions, the oxidation/reduction potential of the sulfurous acid solutions may be modified to stimulate these other bacterial, archaeal and methanogen populations. For example, in the event that aerobic conditions are required for activation of methanogenesis where cyanobacteria and microalgae, fungi, lichens and mosses are present as well as an array of prokaryotic species from biological soil crusts, oxygen and additional acid may be injected into the sulfur dioxide (SO₂) water to provide H⁺, SO₂, SO₃ ⁼, HSO₃ ⁻, dithionous acid (H₂S₂O₄), and other sulfur intermediate reduction products forming a sulfur dioxide treated water to insure that the electrical conductivity level of the sulfur dioxide treated water is sufficient to accept electrons to create an oxidizing solution. The oxidation/reduction potential in millivolts for oxidizing is between −50 to −150 mV under aerated conditions with sufficient free oxygen, alkalinity, pH, temperature and time.

The production of methane is thus adjusted via biostimulation at the oxidation/reduction potentials required by bacterial, archaeal and methogen populations for optimal gas production. This is accomplished by pH adjustment using additional acid and oxygen if required for oxidation to increase gas production volumes. Conversely, additional acid and oxygen is omitted if required for reduction to increase as production volumes. Therefore, a single sulfurous acid solution is used with sub bituminous coal beds and selectively adjusted to generate and increase the its production from immature source-rocks as well as shale deposits.

Standard as measuring equipment is used to measure the methane production under various oxidation and reduction conditions. Periodic sampling of the sub bituminous coal and shale bed sulfurous waters to determine the type of bacterial populations is often included. Core samples or the withdrawal of a portion of the coal bed waters from the sulfurous acid injection system is used to extract samples for microbiological analysis. pH meters monitor the sulfurous acid pH, and dissolved oxygen meters and ORP meters are used to measure the dissolved, oxygen and oxidation reduction potentials of the sulfurous acid solutions. As the methane gas production is tracked, the sulfurous acid oxidation/reduction conditions are then adjusted and held at the levels required to optimize methane gas production from the different bacterial, archae and methanogen populations.

To generate microbial gas play, the hydrologic framework may require the natural inoculation with additional microorganisms. Basin margins, where the organic matter is less mature and fractures therein more open are targeted to allow nutrients to penetrate the deposit.

The foregoing method employing sulfurous acid to deliver bacterial, archae and methanogen populations with nutrients under anaerobic or aerobic conditions for biostimulation produces methane and petroleum from kerogen and sub bituminous coal beds are a faster rate than that produced by geophysical production.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing of the synthetic carbon cycle.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a drawing of the synthetic carbon cycle produced by Haeseler & Behar, in their article “Methanogenisis: A Part of the Carbon Cycle with Implication for Unconventional Biogenic Gas Resources” presented at the Natural Gas Geochemistry: Recent Developments, Applications and Technologies seminar May 9-12, 2011 at the AAPG HEDBERG Conference in Beijing. China, which illustrates methanogenisis of the present method acting on organic compounds in fossil fuels to produce methane and hydrocarbon compounds. The present method delivers water, sulfur nutrients, and carbonates to fossil beds under anaerobic or aerobic conditions for biostimulation of the symbiotic consortium of microorganisms to break down organic molecules through anaerobic respiration and fermentation into simple, water-soluble compounds to produce methane and petroleum from the margins of kerogen and sub bituminous coal beds at a faster rate than that produced by geophysical production.

The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope. 

1. A biostimulation method of natural microbial populations active at margins of black shale and coal bed deposits where the organic matter has hydrologic flows there through consisting of: a. injecting sulfur dioxide into water producing H⁺, dissolved SO₂, SO₃ ⁻, HSO₃ ⁻, dithionous acid (H₂S₂O₄), and sulfur intermediate reduction products all referred to as sulfurous acid, and b. applying the sulfurous acid to the black shale and coal bed deposits and adjusting the oxidation potential of the sulfurous acid either: i. with the addition of oxygen and additional acid to effectuate a downhole acidic pH and an oxidation reduction potential of between −50 and −150 mV to create an oxidizing solution to provide aerobic conditions to stimulate aerobic microbial consortia to produce methane; or ii. without the addition of additional oxygen and additional acid to effectuate a downhole acidic pH and an oxidation reduction potential of between +50 and −100 mV to create a reducing solution to provide anaerobic conditions to stimulate anaerobic syntrophic bacteria and methanogenic archaea microbial consortia to produce methane; the sulfurous acid applied sufficiently to: ci. reduce bicarbonate and carbonate buildup to produce CO₂, which drives the production of methane by chemoautotrophic assimilation of CO₂ by hydrogen consuming methanogens, cii. increase porosity and flows through the black shale and coal bed deposits, and ciii. provide dissolved SO₂, SO₃ ⁼, HSO₃ ⁻, and dithionous acid (H₂S₂O₄) and sulfur intermediate reduction products to produce soluble bicarbonates and carbonate nutrients at the oxidation reduction potential conducive to the growth of microbial consortia to produce methane.
 2. (canceled)
 3. The biostimulation method according to claim 1, further comprising adding supplemental nutrients to the sulfurous acid.
 4. The biostimulation method according to claim 1, further comprising adding syntrophic bacteria and/or cyanobacteria and methanogenic archaea to the sulfurous acid to inoculate the black shale and coal bed deposits microbial consortia. 